Method and apparatus for characterizing process control equipment coupling integrity

ABSTRACT

In a process plant, a first series of measurements from a coupling interface are received. The first series of measurements are stored. A second series of measurements from a coupling interface are received. The second series of measurements. The first series and second series of measurements are compared. An indication of loss of clamping force is generated if the first series of measurements deviates from the second series of measurements.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to a process plants and, more particularly to monitoring the integrity of process plant components.

SUMMARY OF THE DISCLOSURE

In accordance with one exemplary aspect, a method for indicating loss of clamping force includes receiving a first series of measurements made at a coupling interface, storing the first series of measurements, receiving a second series of measurements made at the coupling interface, storing the second series of measurements, comparing the first series and second series of measurements and generating an indication if the first series of measurements deviates from the second series of measurements.

In accordance with another exemplary aspect, a method of indicating loss of clamping force includes receiving impedance measurements by using a plurality of electrical signals at a plurality of frequencies. In accordance with yet another exemplary aspect, a method receives impedance measurements performed at frequencies that are generally in the range of 30 KHz to 400 KHz. The frequencies are applied to a PZT sensor bonded to the coupling interface, in accordance with an exemplary aspect.

In accordance with yet another exemplary aspect, a method of indicating loss of clamping force includes receiving reflectance measurements made at a plurality of wavelengths. In accordance with yet another exemplary aspect, a method receives reflectance measurements performed at wavelengths range from 0.1 nanometers (nm) to 106 nm. The reflectance measurements made with a FBG sensor located in a gasket disposed between the coupling interface, in accordance with an exemplary aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary block diagram of a process plant having a distributed control and maintenance network including one or more operator and maintenance workstations, controllers, field devices and supporting equipment, in which a fault detection and isolation system may be implemented;

FIG. 2 is a block diagram of a statistical data collection and analysis block implementing a method to detect loss of clamping force at a coupling interface.

FIG. 3 is a cross-sectional diagram of a coupling interface adapted with sensors to detect loss of clamping force at the coupling interface.

DETAILED DESCRIPTION

Referring now to FIG. 1, an example process plant 10 in which a fault detection and isolation system may be implemented includes a number of control and maintenance systems interconnected together with supporting equipment via one or more communication networks. In particular, the process plant 10 of FIG. 1 includes one or more process control systems 12 and 14. The process control system 12 may be a traditional process control system such as a PROVOX or RS3 system or any other control system which includes an operator interface 12A coupled to a controller 12B and to input/output (I/O) cards 12C which, in turn, are coupled to various field devices such as analog and Highway Addressable Remote Transmitter (HART®) field devices 15. The process control system 14, which may be a distributed process control system, includes one or more operator interfaces 14A coupled to one or more distributed controllers 14B via a bus, such as an Ethernet bus. The controllers 14B may be, for example, DeltaVTM controllers sold by Emerson Process Management of Austin, Tex. or any other desired type of controllers. The controllers 14B are connected via I/O devices to one or more field devices 16, such as for example, HART® or Fieldbus field devices or any other smart or non-smart field devices including, for example, those that use any of the PROFIBUS®, WORLDFIP®, Device-Net®, AS-Interface and CAN protocols. As is known, the field devices 16 may provide analog or digital information to the controllers 14B related to process variables as well as to other device information. The operator interfaces 14A may store and execute tools available to the process control operator for controlling the operation of the process including, for example, control optimizers, diagnostic experts, neural networks, tuners, etc.

Still further, maintenance systems, such as computers executing the AMS application or any other device monitoring and communication applications may be connected to the process control systems 12 and 14 or to the individual devices therein to perform maintenance and monitoring activities. For example, a maintenance computer 18 may be connected to the controller 12B and/or to the devices 15 via any desired communication lines or networks (including wireless or handheld device networks) to communicate with and, in some instances, reconfigure or perform other maintenance activities on the devices 15. Similarly, maintenance applications 17 and 19 such as the AMS application may be installed in and executed by one or more of the user interfaces 14A associated with the distributed process control system 14 to perform maintenance and monitoring functions, including data collection related to the operating status of the devices 16.

The process plant 10 also includes various rotating equipment 20, such as turbines, motors, etc. which are connected to a maintenance computer 22 via some permanent or temporary communication link (such as a bus, a wireless communication system or hand held devices which are connected to the equipment 20 to take readings and are then removed). The maintenance computer 22 may store and execute known monitoring and diagnostic applications 23 provided by, for example, CSI (an Emerson Process Management Company) or other any other known applications used to diagnose, monitor and optimize the operating state of the rotating equipment 20. Maintenance personnel usually use the applications 23 to maintain and oversee the performance of rotating equipment 20 in the plant 10, to determine problems with the rotating equipment 20 and to determine when and if the rotating equipment 20 must be repaired or replaced. In some cases, outside consultants or service organizations may temporarily acquire or measure data pertaining to the equipment 20 and use this data to perform analyses for the equipment 20 to detect problems, poor performance or other issues effecting the equipment 20. In these cases, the computers running the analyses may not be connected to the rest of the system 10 via any communication line or may be connected only temporarily.

Similarly, a power generation and distribution system 24 having power generating and distribution equipment 25 associated with the plant 10 is connected via, for example, a bus, to another computer 26 which runs and oversees the operation of the power generating and distribution equipment 25 within the plant 10. The computer 26 may execute known power control and diagnostics applications 27 such as those provided by, for example, Liebert and ASCO or other companies to control and maintain the power generation and distribution equipment 25. Again, in many cases, outside consultants or service organizations may use service applications that temporarily acquire or measure data pertaining to the equipment 25 and use this data to perform analyses for the equipment 25 to detect problems, poor performance or other issues affecting the equipment 25. In these cases, the computers (such as the computer 26) running the analyses may not be connected to the rest of the system 10 via any communication line or may be connected only temporarily.

As illustrated in FIG. 1, a computer system 30 implements at least a portion of a fault detection and isolation (FDI) system 35 using a principal component analysis (PCA) on statistical signature data. Statistical signature data may include, but is not limited to, statistical measures such as a mean, a mean change, a median, a median change, a standard deviation, a standard deviation change, a variance, a skewness, a kurtosis, a root-mean-square (RMS), a rate of change, a range, a minimum, a maximum and the like. In particular, the computer system 30 stores and implements a configuration and data collection application (CDCA) 38, one or more viewing or interface applications 40, a PCA module 42 which may include statistical processing blocks and provides multivariate statistical analysis, and a fault detection module 44. The system 30 also stores a statistical process monitoring database 43 that stores statistical signature data generated within certain devices within the process. Generally speaking, the configuration and data collection application 38 configures and communicates with each of a number of statistical data collection and analysis blocks (not shown in FIG. 1) located in the field devices 15, 16, the controllers 12B, 14B, the rotating equipment 20 or its supporting computer 22, the power generation equipment 25 or its supporting computer 26 and any other desired devices and equipment within the process plant 10, to thereby collect statistical signature data (or in some cases, raw process variable data) from each of these blocks with which to perform fault detection and isolation. The configuration and data collection application 38 may be communicatively connected via a hardwired bus 45 to each of the computers or devices within the plant 10 or, alternatively, may be connected via any other desired communication connection including, for example, wireless connections, dedicated connections which use OPC, intermittent connections, such as ones which rely on handheld devices to collect data, etc. Likewise, the configuration and data collection application 38 may obtain data pertaining to the field devices and equipment within the process plant 10 via a LAN or a public connection, such as the Internet, a telephone connection, etc. (illustrated in FIG. 1 as an Internet connection 46) with such data being collected by, for example, a third party service provider. Further, the configuration and data collection application 38 may be communicatively coupled to computers/devices in the plant 10 via a variety of techniques and/or protocols including, for example, Ethernet, Modbus, HTML, XML, proprietary techniques/protocols, etc. Thus, although particular examples using OPC to communicatively couple the configuration and data collection application 38 to computers/devices in the plant 10 are described herein, one of ordinary skill in the art will recognize that a variety of other methods of coupling the configuration and data collection application 38 to computers/devices in the plant 10 can be used as well. The collected data may be reference data, associated with a known normal or known abnormal process condition, or monitored data, for which the process condition is unknown. The configuration and data collection application 38 may generally store the collected data in the database 43.

Although the process plant 10 is shown as including an FDI system 35, it should be understood that the FDI system 35 is not limited to detecting of existing faults or other abnormal conditions, but may also predict the occurrence of an abnormal condition, examples of which as disclosed further below. As such, the FDI system 35 may be utilized to detect existing faults and other abnormal conditions within the process as part of fault detection and isolation, and to predict the occurrence of faults and other abnormal conditions within the process as part of abnormal condition prevention. For example, the fault detection module 44 may be utilized to detect existing and predicted abnormal conditions, as described herein.

Further, although PCA is primarily disclosed as a multivariate statistical analysis technique that may be employed, it should be understood that PCA is provided only as an example, and PCA is explained in order to better understand the fault detection and abnormal condition prevention methodology employed. As such, other multivariate statistical analysis techniques may also be utilized, including, but not limited to partial least squares (PLS), principal component regression (PCR), discriminant analysis and canonical variate analysis (CVA). Different multivariate statistical analysis techniques may be utilized depending on the abnormal condition being detected. For example, while PCA may be utilized for both detecting and predicting abnormal conditions, PCA may be utilized to detect the occurrence of abnormal conditions whereas PLS and/or PCR may be utilized to predict the occurrence of abnormal conditions. As such, the FDI system 35 may include additional modules for different multivariate analysis techniques and/or the PCA module 42 may be replaced with a PLS module, a PCR module, a discriminant analysis module, a CVA module or any other multivariate statistical analysis module.

Referring again to FIG. 1, once the configuration and data collection application 38 collects the statistical signature (or raw process variable) data, the PCA module 42 may conduct multivariate statistical analysis to process the data in one of several ways. The PCA module 42 may use the collected statistical signature data as reference data associated with a normal condition and one or more abnormal conditions, to determine principal components associated with more than one process condition, and form a loading matrix associated with the combined conditions. Alternatively, the PCA module 42 may use the collected statistical signature data as reference data, associated with a normal or abnormal process condition, to determine principal components associated with the process condition, and form a loading matrix associated with each condition. The PCA module 42 may also use raw process variable data, if associated with a known normal or known abnormal process condition, to compute reference statistical signature data from which to determine principal components associated with one or more process conditions. Raw process variable data may include, but is not limited to, data measured from the process including data measured from devices within the process such as temperature, pressure, flow rate, position and the like. The PCA module 42 may further store the results of the principal component analysis, as well as the reference statistical signature data in the database 43 for use by the fault detection module 44 or the viewing application 40. Additionally, the PCA module 42 may determine, using parallel analysis or another similar method, how many principal components calculated by the PCA module 42 to retain for use by the fault detection module 44.

The fault detection module 44 analyzes monitored statistical signature (or raw process variable) data, using the results of the principal component analysis performed by the PCA module 42, to determine the existence or future existence of an abnormal process condition. As described in detail below, the fault detection module 44 may project the monitored statistical signature or raw process variable data into the score matrix, using the loading matrix previously determined by the PCA module 42. The fault detection module 44 may then generate one or more alerts or alarms for operators or maintenance personnel based on the results of the analysis, or otherwise alert process operators or maintenance personnel that an abnormal condition exists or is predicted. Likewise, the fault detection module 44 may store the results of the analysis, including faults detected, alerts or alarms generated, and data projected onto the score matrix (described below), in the database 43 or communicate the results to the viewing and interface application 40.

The viewing and interface application 40 includes an interface for plant personnel such as configuration engineers, process control operators, maintenance personnel, plant managers, supervisors, etc. to view alerts and alarms generated by the fault detection module 44. The viewing application 40 may also include an interface that allows manipulation of various process control parameters, manipulation of the PCA module 42 and the fault detection module 44, and display of relevant data including statistical signature data, raw process variable data, auto-scaled data, data mapped on to score matrices or any other data useful to display for plant personnel.

The viewing and interface application 40 may provide a graphical user interface (GUI) that is integrated with the system 30, or more particularly with the FDI system 35, to facilitate a user's interaction with the monitoring capabilities provided by the FDI system 35. However, before discussing the GUI in greater detail, it should be recognized that the GUI may include one or more software routines that are implemented using any suitable programming languages and techniques. Further, the software routines making up the GUI may be stored and processed within a single processing station or unit, such as, for example, a workstation, a controller, etc. within the plant 10 or, alternatively, the software routines of the GUI may be stored and executed in a distributed manner using a plurality of processing units that are communicatively coupled to each other within the FDI system 35.

Preferably, but not necessarily, the GUI may be implemented using a familiar graphical windows-based structure and appearance, in which a plurality of interlinked graphical views or pages include one or more pull-down menus that enable a user to navigate through the pages in a desired manner to view and/or retrieve a particular type of information. The features and/or capabilities of the FDI system 35 may be represented, accessed, invoked, etc. through one or more corresponding pages, views or displays of the GUI. Furthermore, the various displays making up the GUI may be interlinked in a logical manner to facilitate a user's quick and intuitive navigation through the displays to retrieve a particular type of information or to access and/or invoke a particular capability of the FDI system 35.

Those of ordinary skill in the art will appreciate that the FDI system 35 described herein may operate alone or in cooperation with other systems, including other fault detection and abnormal condition prevention systems. Likewise, the individual applications 38, 40, 42, and 44 described herein as part of the FDI system 35 may operate cooperatively with other applications (not shown) to detect faults, generate alerts and alarms, provide data to plant personnel, allow process or device configuration or any combination of the above.

Referring again to FIG. 1, valves 15 and 16 for example may be coupled to external piping and process control equipment with fasteners such as bolts. In one scenario, a gasket may be provided between the coupling surfaces or flanges of the valves for example and external process control equipment coupling surfaces. In such a scenario, the coupling surfaces are adapted with openings through which fasteners such as bolts may be placed. In such a scenario, the nut may be tightened around the threaded end of a bolt.

In some scenarios, a bolt and a corresponding nut may be tightened with a prescribed torque or strain. In such scenarios, the nut and the head of the bolt exert a force on the coupling surfaces, the flanges for example. A nut and/or bolt may loosen because of operating environment, process conditions, age, and human error for example. In this scenario, the force exerted on the coupling surfaces by the head of the bolt and the nut changes. This translates to a loss of clamping force. This is referred to as loss of pre-load on a bolted joint. Loss of pre-load increases the risk of gasket failure.

In some instances, the flange of a valve 15 for example may be adapted with sensors to measure the force applied by a nut and bolt for example, on the flange. Such sensors include but are not limited to piezoelectric (PZT) sensors, Fiber Bragg grating (FBG) sensors for example. The sensors may be bonded to the flange, in some instances. In other instances, the flange may be manufactured with the sensor in the flange. In such instances the flange may be provided with a port to access the sensor. In still other instances, a FBG sensor may be located in a gasket which is interposed between the coupling surfaces which are held in place with a fastener. In this instance, the gasket may be adapted to accept a FBG sensor for example and to provide access to the FBG sensor.

In other instances a valve 15 may be coupled with valve mating flanges. In some other instances a valve 15 may be coupled with process plant equipment with a bonnet joint. In still other instances, process equipment may be controlled with actuators. In these instances actuators interface with process equipment including valves with actuator diaphragm casing joints.

In instances described above, an FBG sensor or an impedance sensor may be disposed at a valve mating flange using techniques described above. In some other instances, an FBG sensor or an impedance sensor may be used at a bonnet joint. In still other instances, an FBG sensor or an impedance sensor may used an actuator diaphragm casing joint.

In certain instances, sensors are monitored and controlled by statistical data collection and analysis blocks which may be located at valve positioners or the valve bodies 15 for example. In this instance, the sensor is adapted with a connector bus which is adapted to receive power, excitation signals and transmit electrical sensor data to the data collection block. In other instances the sensors may be monitored and controlled from I/O cards 12C for example. In some instances the data received by the data collection and analysis block is also received by the FDI 35.

In instances where a FBG sensor is employed in the gasket for example, the excitation signal comprises light at a characteristic wavelength. The FBG sensor measures the level of light reflected at the gratings of the FBG sensor. A loss of pre-load on the bolt shifts the refractive index of the gratings in the FBG sensor. A change of refractive index of an FBG sensor changes the level of light reflected at the characteristic wavelength. A change in the level of reflected light received at the characteristic wavelength indicates a loss of pre-load on a bolt in an embodiment. In some embodiments, the degree of change in level of the reflected lights corresponds to reduction on force at a coupling interface.

In some embodiments the PCA module 42 analysis the data from a sensor bonded to a flange of a valve. In this embodiment, the PCA module 42 provides real-time monitoring of the load exerted by a fastener on a flange of a valve. Detecting loss of pre-load or a loosening of a fastener may be automated by the PCA module 42 without requiring a visual inspection of the fastener. The PCA module 42 in this embodiment creates a signature from the data received from the sensor bonded to the flange of the valve. In other embodiments the sensor data from a flange is analyzed by an AMS system for example.

FIG. 2 is a block diagram of a statistical data collection and analysis block located in the field devices 15, 16 for example that implements an embodiment 200 to detect loss of pre-load of a fastener at a flange of a valve 16, for example. In an embodiment, the sensor 204 is a piezoelectric (PZT) sensor. PZT sensor 204 is attached to a flange of a valve 202 using a suitable bonding technique. The PZT sensor 204 is made from a piezoceramic material such as lead zirconate titanate, in this embodiment. One skilled in the art will recognize that any material exhibiting a piezoelectric effect may be used as a sensor. The PZT sensor 204 is soldered to the flange 202, in this embodiment. In some other embodiment, the sensor 204 is attached to the flange 202 with a bonding agent or adhesive. In yet other embodiment, the sensor 204 is integrated in the flange 202. In an embodiment, access to the sensor 204 is provided through connector 212.

An excitation module (EM) 206 provides the PZT sensor 204 with an excitation frequency. The microcontroller 210 controls the EM 206. The microcontroller 210 communicates with the EM 206 over a serial 12C bus in this embodiment. The EM 206 is adapted to generate electrical signals having excitation frequencies that range from 30-400 Kilohertz (KHz), in this embodiment. In this embodiment, the microcontroller 210 communicates to the EM 206 the desired excitation frequency to be generated. Also, in this embodiment, the microcontroller 210 provides the EM 206 the desired voltage level for the electrical signals generated by the EM 206. In another embodiment, the microcontroller 210 provides the EM 206 the range of excitation frequencies to be generated. In this embodiment, the EM 206 sequentially generates electrical signals having excitation frequencies corresponding to the range of excitation frequencies provided by the microcontroller.

In an embodiment, the EM 206 comprises a digital to analog convertor (DAC) electrical coupled to a voltage controlled oscillator (VCO). In this embodiment, the DAC receives a digital representation of the excitation frequency from the microcontroller 210. The DAC produces an analog voltage which corresponds to the excitation frequency for electrical signal to be generated. The VCO generates the excitation frequency that corresponds to the analog voltage produced by the DAC, in this embodiment. In some other embodiments, the EM 206 is adapted to generate electrical signals complex having two or more excitation frequencies.

On receiving an electrical signal from the EM 206, the PZT 204 generates an electrical current that corresponds to the impedance measure of the combined PZT 204, flange 202 and a fastener (not shown). The electrical current generated by the PZT 204 changes as the excitation frequency of the electrical signal generated by the EM 206 is changed.

The electrical current generated by the PZT 204 is received by a signal conditioning and measuring unit (SCMU) 208. The SCMU 208 communicates with the microcontroller 210 over a serial I2C bus. The microcontroller 210 instructs the SCMU 208 to sample the electrical current generated by the PZT 204. The SCMU 208 comprises signal conditioning circuitry and electronics. Such circuitry includes but is not limited to current to voltage convertors, low noise amplifiers (LNA), band pass and notch filters. One skilled in the art will recognize that the impedance measure comprises a real and an imaginary component. The SCMU 208 generates a digital representation of the real component of the electrical current that corresponds to the impedance measure of the combined PZT 204, valve flange 202 and a fastener, in this embodiment. The digital representation of the impedance measure is received by the microcontroller 210. In an embodiment the SCMU 208 comprises an analog to digital convertor (ADC). In this embodiment, the ADC is a successive approximation ADC. In another embodiment, a dual slope ADC is employed.

In an embodiment, the microcontroller 210 communicates to the EM 206 the desired excitation frequency of the electrical signal to be generated. The EM 206 generates an electrical signal at the excitation frequency and applies the electrical signal to the PZT 204. The microcontroller 210 instructs the SCMU 208 to sample the electrical current generated by the PZT 204 in response to the electrical signal. The digital representation is received by the microcontroller 210. The microcontroller 210 communicates to the EM 206 a different excitation frequency for the electrical signal to be generated and instructs the SCMU 208 to sample the electrical current generated by the PZT 204 in response to receiving the electrical signal generated at the different excitation frequency. In this embodiment, the microcontroller sequentially communicates to the EM 206 excitation frequencies that range from 30-400 KHz in steps of 1 KHz for example 30 KHz, 31 KHz . . . , 399 KHz, 400 KHz. After communicating each excitation frequency to the EM 206, the microcontroller 202 instructs the SCMU 208 to sample the electrical current generated by the PZT 204 in response to receiving the electrical signal generated at the different excitation frequency. Thus, the microcontroller 210 creates an impedance record of the impedance measure of the combined PZT 204, flange body 202 and the fastener and the corresponding excitation frequencies of the electrical signals generated by the EM 206.

Referring to FIG. 1, the microcontroller 210 transmits the record comprising impedance measures and the corresponding excitation frequencies to a computer system 30, in an embodiment. In this embodiment, the microcontroller 210 implements the CAN protocol to communicate with the computer system 30. In this embodiment, the CDCA 38 implemented as a part of fault detection and isolation (FDI) system 35 which in turn is implemented at computer system 30 instructs the microcontroller 210 to create an impedance record. The CDCA 38 instructs the microcontroller 210 of the start excitation frequency, the end excitation frequency and the incremental change in frequency. The CDCA 38 receives the impedance record from the microcontroller 210. In this embodiment, the CDCA 38, stores the impedance record in the database 43.

The PCA module 42 retrieves the stored impedance record from the database 43 and applies curve fitting techniques to the impedance record. In an embodiment, the PCA module 42 generates a nth order polynomial fit of the impedance record. The PCA module 42 stores the coefficients of the polynomial in the database 43. In an embodiment, these coefficients correspond to the impedance signature of the flange 202, for example. In other embodiment, the impedance record serves as the impedance signature of the flange 202, for example.

In an embodiment, the CDCA 38 periodically instructs the microcontroller 210 to create an impedance record. The CDCA 38 receives the impedance record from the microcontroller 210.

In an embodiment, the CDCA 38 receives the impedance record and retrieves a prior stored impedance record for the flange 202, for example. In this embodiment the CDCA 38 communicates the received impedance record and the retrieved impedance record to the PCA 42. The PCA 42 compares the impedance records to detect a change in the impedance signature. In an embodiment, a change is signaled if the coefficients calculated for a polynomial fit of the impedance record deviate from preset thresholds for the coefficients. In some embodiments, the PCA 42 computes an average of the historical impedance records stored in database 43 for a flange 202, for example. The average of the impedance records is compared with a received impedance record to detect deviations from the average. In still other embodiments, the PCA 42 computes a standard deviation of an impedance record received from the CDCA 38 from the historical impedance records stored in the database 43.

In this embodiment, a user specifies a threshold standard deviation value in the viewing and interface application 40 that is integrated with the system 30, or more particularly with the FDI system 35. If the received impedance record deviates from the user-specified threshold, an indication in the form of a visual cue and an audible sound are generated in this embodiment. In this embodiment, a deviation indicates a loss of pre-load or clamping force on the flange 200 because of a loosening of the bolt.

In an embodiment, a user instructs the microcontroller 210 to create an impedance record through the viewing and interface application 40. In some embodiments, the FDI system 35 provides a user with an indication corresponding to the useful life of the flange 202, for example. In this embodiment, the indication is provided via the viewing and interface application 40.

In another embodiment, the sensor 204 is a FBG sensor. A FBG sensor comprises a glass fiber which is manufactured with gratings etched in the core of the glass fiber. The refractive index of the gratings of a FBG sensor is designed to reflect light of a characteristic wavelength. Compressing the FBG sensor along its axis, for example, changes the refractive index of the gratings. In other situations, changes in the ambient temperature causes a change in the refractive index of the gratings.

In each instance, the change in the refractive index shifts the characteristic wavelength of the light which is reflected at the gratings. In this instance, the FBG sensor may be employed to measure the force applied by a fastener employed to couple a valve flange to a process control equipment connector for example. As described previously, an FBG sensor may be employed at an actuator diaphragm, for example.

In an embodiment, the sensor 204 is located in a gasket between the flanges. The EM 206 in this embodiment comprises a light source. The light source is capable of generating light across a wide range of wavelengths. The wavelengths of the light generated may range from infra-red (IR), visible through ultra-violet (UV). In another embodiment, the light source is a single wavelength laser light source. The light generated by the EM 206, in an embodiment, is coupled to the FBG sensor with a suitable connector or adapter 212. In this embodiment, the connector 212 is also adapted to receive a light sensor. Light sensors include but are not limited to photo diodes, photo transistors, light dependent resistor or any other suitable transducer capable of converting light to an electrical signal. In some embodiments, the intensity of the light may be modulated.

In some embodiments, a light filter module may be interposed between the light sensor and the FBG sensor. A light filter selectively passes light having a range of wavelengths. The light filter module may include a variety of selectable light filters each of which selectively pass light having a different range of wavelengths. In some embodiments, the range of wavelengths overlap. In this embodiment, a microcontroller 210 sequentially adjusts the light filter module to select a different light filter. After each adjustment, the microcontroller 210 triggers the SCMU 208 to receive the electrical signal generated by the light sensor. The electrical signal generated corresponds to the level of light for a range of wavelengths received at the light sensor. Of course, the range of wavelengths corresponds to the selected light filter, in this embodiment. In an embodiment, the microcontroller 210 generates a reflectance record from the measurements received by the SCMU at different ranges if wavelengths. A reflectance record may include the intensity of the light received at the sensor for different ranges of wavelengths. In some embodiments, the microcontroller may receive an indication of the temperature at the flange. In this embodiment, the microcontroller 210 compensates for temperature related variations in the signal level of the reflected light.

Referring to FIG. 1, the microcontroller 210 transmits the record comprising reflectance measurements and the corresponding wavelengths to a computer system 30, in an embodiment. In this embodiment, the microcontroller 210 implements the CAN protocol to communicate with the computer system 30. In this embodiment, the CDCA 38 implemented as a part of fault detection and isolation (FDI) system 35 which in turn is implemented at computer system 30 instructs the microcontroller 210 to create an reflectance record. The CDCA 38 instructs the microcontroller 210 of the start excitation frequency, the end excitation frequency and the incremental change in frequency. The CDCA 38 receives the reflectance record from the microcontroller 210. In this embodiment, the CDCA 38, stores the reflectance record in the database 43.

The PCA module 42 retrieves the stored reflectance record from the database 43 and applies curve fitting techniques to the reflectance record. In an embodiment, the PCA module 42 generates a nth order polynomial fit of the reflectance record. The PCA module 42 stores the coefficients of the polynomial in the database 43. In an embodiment, these coefficients correspond to the reflectance signature of the flange 202, for example. In other embodiment, the reflectance record serves as the reflectance signature of the flange 202, for example.

In an embodiment, the CDCA 38 periodically instructs the microcontroller 210 to create an reflectance record. The CDCA 38 receives the reflectance record from the microcontroller 210.

In an embodiment, the CDCA 38 receives the reflectance record and retrieves a prior stored reflectance record for the flange 202, for example. In this embodiment the CDCA 38 communicates the received reflectance record and the retrieved reflectance record to the PCA 42. The PCA 42 compares the reflectance records to detect a change in the reflectance signature. In an embodiment, a change is signaled if the coefficients calculated for a polynomial fit of the reflectance record deviate from preset thresholds for the coefficients. In some embodiments, the PCA 42 computes an average of the historical reflectance records stored in database 43 for a flange 202, for example. The average of the reflectance records is compared with a received reflectance record to detect deviations from the average. In still other embodiments, the PCA 42 computes a standard deviation of an reflectance record received from the CDCA 38 from the historical reflectance records stored in the database 43.

In this embodiment, a user specifies a threshold standard deviation value in the viewing and interface application 40 that is integrated with the system 30, or more particularly with the FDI system 35. If the received reflectance record deviates from the user-specified threshold, an indication in the form of a visual cue and an audible sound are generated in this embodiment. In this embodiment, a deviation indicates a loss of pre-load on the flange 200 because of a loosening of the bolt.

In an embodiment, a user instructs the microcontroller 210 to create an reflectance record through the viewing and interface application 40. In some embodiments, the FDI system 35 provides a user with an indication corresponding to the useful life of the flange 202, for example. In this embodiment, the indication is provided via the viewing and interface application 40.

FIG. 3 is an example coupling interface 300, comprising bolt 302, nut 304, coupling surfaces 306, 308 and gasket 310. In this example, a FBG sensor 312 is located in the gasket 310 disposed between the coupling surfaces 306 and 308. The reflectance of the sensor 312 changes when the clamping force exerted on the coupling surfaces 306 and 308 by the bolt 302 and 304 decreases. Referring to FIG. 1, the FDI 35, detects this change in reflectance. PZT sensors 314 and 316 are bonded to the coupling surface 306 and nut 302 respectively. Impedance measurements received from sensors 314 and 316 indicate a loss of clamping force in this embodiment. In some embodiments, either one or only some of the sensors 312, 314 or 316 may be disposed at the coupling interface.

In other embodiments, the PZT sensor and FBG sensor are manufactured as washers or gaskets. In these embodiments, the washers are disposed between the coupling interfaces. The methods described here may also be used to detect a loss of clamping force on a seal or diaphragm used in a process plant. The embodiments described here may also be used to detect a loosening of other coupling interfaces commonly employed in a process plants for example including but not limited to stem connectors, actuator yoke locknut area or bolting flange.

In other embodiments, a FDI 35 may interpret reflectance results to determine the temperature at the coupling surface where the FBG sensor is disposed. In other embodiments, the impedance or reflectance reports may be interpreted by an FDI 35 to report the torque being applied to the fastener at the coupling surface when a valve 15 for example is first being installed in a process plant. In such an embodiment, improper fastening conditions may be reported.

In other embodiments, strain gauges may be employed at coupling interfaces to determine pipe line bolting forces or internal valve body pressures. Referring to FIG. 2, the sensor 204 in these embodiments comprises a transducer adapted to measure strain or pressure for example.

In some embodiments, the FDI 35 implements calibration routines to allow the generation of a reflectance or impedance curve when the valve 15 is first installed. In an embodiment, the calibration routine comprises a component of a general valve calibration software.

The embodiments described above with reference to a nut and bolt may also be adapted to indicate a change in characteristics in a valve bonnet/gasket joint. In some other scenarios, the embodiments described previously may be adapted to monitor the integrity of a pneumatic actuator casing joint. In these embodiments a FBG sensor may be disposed which includes the air diaphragm which is pinched between the two actuator casing halves. 

What is claimed is:
 1. A method implemented at a fault detection and isolation (FDI) system for indicating loss of clamping force at a coupling interface of a pair of flanges, the method comprising; receiving at the FDI system, a first series of measurements made at a coupling interface; storing the first series of measurements; receiving at the FDI system a second series of measurements made at the coupling interface; storing the second series of measurements; generating a first curve based on the first series of measurements and a second curve based on the second series of measurements; determining a first plurality of coefficients for the first curve and a second plurality of coefficients for the second curve; comparing the first plurality of coefficients for the first curve and the second plurality of coefficients for the second curve to determine if the first series of measurements deviates from the second series of measurements; generating an indication if the first series of measurements deviates from the second series of measurements.
 2. The method of claim 1, wherein the first series of measurements and the second series of measurements comprise impedance measurements made using a plurality of electrical signals at a plurality of frequencies, the impedance measurements made in response to the FDI transmitting a first request for the first series of impedance measurements and a second request for the second series of impedance measurements.
 3. The method of claim 2, wherein each of the plurality of frequencies range from 30 Kilohertz (KHz) to 400 KHz.
 4. The method of claim 2, including applying each of the plurality of electrical signals to the coupling interface through a piezoelectric (PZT) sensor.
 5. The method of claim 4, including bonding the PZT sensor to the coupling interface.
 6. The method of claim 4, including bonding the PZT sensor to the coupling interface with an adhesive.
 7. The method of claim 1, wherein the coupling interface is one of a flange joint, a valve bonnet joint, or an actuator casing joint.
 8. The method of claim 1, wherein the first series of measurements and the second series of measurements comprise acoustic measurements.
 9. The method of claim 8, wherein the first series and the second series of acoustic measurements comprise measurements received from a PZT sensor in response to the FDI transmitting a first request for the first series of acoustic measurements and a second request for the second series of acoustic measurements.
 10. The method of claim 2, wherein transmitting the first request and the second request includes transmitting an indication of at least one of the plurality of frequencies.
 11. An apparatus for detecting loss of clamping force at a coupling interface between a field device and a process plant component, the apparatus comprising: a fault detection and isolation (FDI) system; a sensor coupled to the body of the field device; an excitation module electrically coupled to the sensor; a measurement module electrically coupled to the sensor; an analyzer coupled to the measurement module and configured to generate a first curve based on a first series of measurements by the measurement module and a second curve based on a second series of measurements by the measurement module, the analyzer further configured to determine a first plurality of coefficients for the first curve and a second plurality of coefficients for the second curve and then compare the first plurality of coefficients and the second plurality of coefficients to determine if the first series of measurements deviates from the second series of measurements; and an indicator coupled to the analyzer and configured to generate an indication if the first series of measurements deviates from the second series of measurements.
 12. The apparatus of claim 11, wherein the sensor is a piezoelectric (PZT) sensor.
 13. The apparatus of claim 12, wherein the PZT sensor is coupled to the body of the field device near the coupling interface of the field device with a bonding adhesive.
 14. The apparatus of claim 13, wherein the excitation module is arranged to electrically excite the PZT sensor via the electrical coupling with an electrical signal at a selected frequency, wherein the selected frequency ranges from 30 Kilohertz (KHz) to 400 KHz.
 15. The apparatus of claim 14, wherein the excitation module is arranged to receive an indication of the selected frequency from the FDI.
 16. The apparatus of 15, wherein the measurement module is arranged to transmit data measured from the PZT sensor to the FDI.
 17. A method for indicating loss of clamping force at a coupling interface of a pair of flanges, the method comprising: causing a fault detection and isolation (FDI) system to receive a first series of measurements, wherein each of the measurements of the first series of measurements is made at the coupling interface; in response to receiving the first series of measurements, causing the FDI system to store the first series of measurements; causing the FDI system to receive a second series of measurements, wherein each of the measurements of the second series of measurements is made at the coupling interface; in response to receiving the second series of measurements, causing the FDI system to store the second series of measurements; generating a first curve based on the first series of measurements and a second curve based on the second series of measurements; determining a first plurality of coefficients for the first curve and a second plurality of coefficients for the second curve; comparing the first plurality of coefficients and the second plurality of coefficients to determine if the first series of measurements deviates from the second series of measurements; determining that the first series of measurements deviates from the second series of measurements; and causing the FDI to generate an indication on determining that the first series of measurements deviates from the second series of measurements.
 18. The method of claim 17, wherein the first series of measurements is received in response to causing the FDI system to transmit a first request for the first series of measurements and the second series of measurements is received in response to causing the FDI system to transmit a second request for the second series of measurements.
 19. The method of claim 18, wherein each of the first request and the second request includes an indication of a selected frequency.
 20. The method of claim 19, wherein each of the first series of measurements and the second series of measurements correspond to impedance measurements caused to be made at the coupling interface by exciting a PZT sensor with an electrical signal at the selected frequency, wherein the PZT sensor is bonded to the coupling interface. 